1. Field of the Invention
This invention relates generally to apparatus used to regulate fluid flow in medical devices, and more particularly to check valves for such apparatus.
2. Statement of the Prior Art
For ease of manufacture, there have been proposed many styles of check valves in the prior art. See, for example, U.S. Pat. Nos. 2,462,189 (Hess); 2,497,906 (Peters et al.); 4,141,379 (Manske); and 4,712,583 (Pelmulder et al.); and, a Japanese Application No. 58-77980 (Okumura). Unfortunately, the check valves that are most easily manufactured frequently suffer from weepage and leakage problems, as well as an inability to be variably set for different "cracking pressures". These cracking pressures, as is well known, constitute the pressures at which a check valve will open but below which it will stay closed.
In the administration of medical solutions, check valves are very important. A typical case is where primary lines of such solutions (e.g., saline or dextrose solutions) are administered from intravenous bags through flexible tubing to a patient having an intravenous (IV) needle. Solution is delivered to the patient by any conventional delivery means such as gravity flow, pressure cuffs, syringe pumps or peristaltic pumps. Valves such as disclosed in the aforementioned U.S. Pat. No. 4,712,583 (Pelmulder et al.) are necessary with such systems to provide for careful control in the administration of the solution.
Secondary lines may also be used in the administration of different solutions. For example, saline solution may be administered through the primary line of a system, and at the same time a secondary medication may be administered through a secondary line that is connected by way of a Y-fitting. These systems which employ both a primary and a secondary line may require check valves in both lines, but the particular requirements for each check valve may be different. In valves used for a primary line, for example, an "antireflux" type valve is necessary. The conventional antireflux valve must open very rapidly, yet have a minimum hysteresis in the reverse direction. Accordingly, these antireflux valves are usually complex in their design as well as their manufacture. The Pelmulder et al. patent is indicative of such complex designs.
Check valves which are used in the secondary lines for administration of secondary solutions have different requirements from their antireflux valve counterparts. That is, in this type of "piggyback" medication therapy, the check valves should be preloaded to provide increased cracking pressure while at the same time protecting against the case of occlusion alarms where blockages cause tremendous backflows in the secondary line. Furthermore, check valves used in secondary lines must be capable of preventing a flow of the secondary medication unless and until flow is established in the primary line.
A problem with previous check valves used with apparatus to administer medical solutions is their complexity of design and manufacture. Such complexity can increase their costs, and prevent their adaptation to variable settings. For example, the cracking pressure required of a particular check valve is dependent on the application in which the valve is used. In view of a multitude of applications, a check valve design capable of a multitude of cracking pressures is necessary. Consequently, a need exists for a check valve which is inexpensive and of a design adaptable to variable settings.